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In this paper, we investigate the form factors and impact parameter space parton distribution functions of the $\rho$ meson derived from the generalized parton distributions within the framework of the Nambu--Jona-Lasinio model,employing a proper time regularization scheme. We compare the charge $G_C$, magnetic $G_M$, and quadrupole $G_Q$ form factors with lattice data. The dressed form factors, $G_C^D$ and $G_M^D$, exhibit good agreement with lattice results; however, $G_Q^D$ is found to be harder than what is observed in lattice calculations. The Rosenbluth cross section for elastic electron scattering on a spin-one particle can be expressed through the structure functions $A(Q^2)$ and $B(Q^2)$. Additionally, the tensor polarization $T_{20}(Q^2,\theta)$ can also be formulated in terms of these form factors. We analyze the structure functions $A(Q^2)$, $B(Q^2)$ and tensor polarization function $T_{20}(Q^2,\theta)$; our findings quantitatively align with predicted values across various limits. In impact parameter space, we examine parton distribution functions along with their dependence on longitudinal momentum fraction $x$ and impact parameter $\bm{b}_{\perp}$. The width distributions in impact parameter space reveal that the range of the charge distribution \( q_C(x,\bm{b}_{\perp}^2) \) is the most extensive. In contrast, the transverse magnetic radius falls within a moderate range, while the quadrupole distribution \( q_Q(x,\bm{b}_{\perp}^2) \) demonstrates the narrowest extent., Comment: 10 pages; 23 figures; To be published in Chinese Physics C

An array of the kaon twist-two, three, four generalised transverse momentum dependent parton distributions (GTMDs) has been investigated within the framework of covariant and confining Dyson-Schwinger equations using contact interaction. GTMDs are of great significance as they encompass information regarding both the generalised parton distributions (GPDs) and the transverse momentum dependent parton distributions (TMDs), thus being considered as the parent distribution. From GTMDs, we can derive the twist-two, three, four GPDs and TMDs. GPDs are obtained through the integration of $\bm{k}_{\perp}$ from GTMDs, with a focus on the twist-two GPDs. The first Mellin moments of GPDs yield the form factors of local currents. The second Mellin moments of vector GPDs are related to gravitational form factors. The Wigner distribution can be obtained from a Fourier transform in the transverse space of the GTMDs at skewedness parameter $\xi=0$. The Wigner distributions of an unpolarized, longitudinally polarized, and transversely polarized quark inside the kaon have been calculated. The spin-orbit correlations between a hadron and a quark can be explained based on the phase-space average of Wigner distributions. We investigate the correlation between the longitudinal spin and orbital angular momentum of valence quarks within the pion and kaon. Our findings reveal that $C_z^{u,K}=-0.336$, $C_z^{s,K}=0.242$, and $C_z^{u,\pi}=-0.374$. The parton distribution function in impact parameter space can be derived from the Wigner distribution. The study focuses on the light-front transverse-spin distributions $\rho_u^1\left(\bm{b}_{\bot },\bm{s}_{\perp}\right)$ and $\rho_u^2\left(\bm{b}_{\bot },\bm{s}_{\perp}\right)$, which exhibit distortions, and we calculate their average shift., Comment: 51pages, 58 figures

In this paper, the light-front wave functions (LFWFs) of $\rho$ meson are evaluated in the framework of Nambu--Jona-Lasinio model using the proper time regularization scheme. The transverse momentum dependent parton distributions (TMDs) of the $\rho$ meson are derived from the overlap representations of the LFWFs. We investigate the $\bm{k}_{\perp}$-weighted moments and the $x$-dependent average transverse momentum $\langle k_{\perp}^n(x)\rangle_{\alpha}$ of $\rho$ meson TMDs, $\langle k_{\perp}^n(x)\rangle_{\alpha}$ shows the typical transverse momenta of quark TMDs in our model. Our findings indicate that the average transverse momenta of $\langle k_{\perp}(x)\rangle_{\alpha}$ fall within the range of $[0.3, 0.45]$ GeV, while $\langle k_{\perp}^2(x)\rangle_{\alpha}$ are in the region of $[0.15, 0.30]$ GeV$^2$. Our TMDs and parton distribution function (PDFs) exhibit excellent adherence to positive constraints. The investigation of spin densities within the $\rho$ meson in transverse momentum space reveals axially symmetric distributions for quarks and targets polarized in either longitudinal or transverse directions. Conversely, unpolarized symmetric distributions occur when the quark is longitudinally polarized and the target is transversely polarized, while exhibiting dipolar distortions in the opposite scenario. A comparison between TMDs from LFWFs and those from a covariant approach demonstrates that TMDs from LFWFs more effectively satisfy positive constraints than their counterparts from the covariant approach. Furthermore, the $x$-moments of $\rho$ meson PDFs indicate that $\langle x\rangle_{g_L}$ is larger using LFWFs compared to the covariant approach., Comment: 14 pages, 27 figures, Published in the European Physical Journal C

The Nambu--Jona-Lasinio model is utilized to investigate the pion and kaon photon leading-twist transition distribution amplitudes using proper time regularization. Separately, the properties of the vector and axial vector pion photon transition distribution amplitudes are examined, and the results meet the desired properties. Our study involves sum rule and polynomiality condition. The vector and axial vector pion photon transition form factors that are present in the $\pi^+\rightarrow \gamma e^+ \nu$ process are the first Mellin moments of the pion photon transition distribution amplitudes. The vector transition form factor originates from the internal structure of hadrons, the axial current can be coupled to a pion, this pion is virtual, and its contribution will be present independently of the external hadrons. The kaon transition form factors are similar. The vector form factor's value at zero momentum transfer is determined by the axial anomaly, while this is not the case for the axial one. The vector and axial form factors, as well as the neutral pion vector form factor $F_{\pi \gamma \gamma}(t)$, are depicted. According to our findings, the pion axial transition form factor is harder than the vector transition form factor and harder than the electromagnetic form factor. We also discuss the link between $\pi - \gamma $ and $\gamma - \pi$ transitions distribution amplitudes., Comment: 11 pages, 15 figures. To be published in Chinese Physics C

In this paper, both the unpolarized and the polarized $\rho$ meson generalized parton distributions are investigated in the framework of the Nambu--Jona-Lasinio model using proper time regularization scheme. The symmetry properties of $\rho$ meson generalized parton distributions are checked. The three independent distribution functions in deep inelastic scattering, $F_1(x)$, $b_1(x)$ and $g_1(x)$, and the Sachs-like charge, magnetic, and quadruple form factors $G_C(t)$, $G_M(t)$ and $G_Q(t)$, which are the first Mellin moments of unpolarized generalized parton distributions are obtained. In addition, the $u$ quark axial vector form factors $\tilde{F}_1^u(t)$ and $\tilde{F}_2^u(t)$ related to the axial currents from the polarized generalized parton distributions are studied. The impact parameter dependent parton distribution functions, which are the two-dimensional Fourier transform of generalized parton distributions are studied, too. The obtained $\rho$ meson generalized parton distributions satisfy the required properties well., Comment: 15 pages, 29 figures, accepted for publication in PRD

Pion generalised parton distributions are calculated within the framework of the Nambu--Jona-Lasinio model using different regularization schemes, including the proper time regularization scheme, the three dimensional momentum cutoff scheme, the four dimensional momentum cutoff scheme, and the Pauli-Villars regularization scheme. Furthermore, we check the theoretical constraints of pion generalised parton distributions required by the symmetries of quantum chromodynamics in different regularization schemes. The diagrams of pion parton distribution functions are plotted, in addition, we evaluate the Mellin moments of generalised parton distributions, which related to the electromagnetic and gravitational form factors of pion. Pion generalised parton distributions are continuous but not differential at $x=\pm \,\xi$, when considering the effect of D-term, generalised parton distributions become not continuous at $x=\pm \,\xi$ in all the four regularization schemes. Generalised parton distributions in impact parameter space are considered, the width distribution of $u$ quark in the pion and the mean-squared $\langle \mathbf{b}_{\bot}^2\rangle_{\pi}^u$ are calculated. The light-front transverse-spin distributions are studied, when quark polarized in the light-front-transverse $+\,x$ direction, the transverse-spin density is no longer symmetric around $(b_x=0,b_y=0)$, the peaks shift to $(b_x=0,b_y>0)$, we compare the average transverse shift $\langle b_{\bot}^y\rangle_1^u$ and $\langle b_{\bot}^y\rangle_2^u$ in different regularization schemes. The light-cone energy radius $r_{E,LC}$ and the light-cone charge radius $r_{c,LC}$ are also evaluated, we find that in the proper time regularization scheme the values of these quantities are the largest, in the three dimensional momentum cutoff scheme they are the smallest., Comment: 34 pages, 39 figures

Pion and kaon structural properties provide insights into the emergence of mass within the Standard Model and attendant modulations by the Higgs boson. Novel expressions of these effects, in impact parameter space and in mass and pressure profiles, are exposed via $\pi$ and $K$ generalised parton distributions, built using the overlap representation from light-front wave functions constrained by one-dimensional valence distribution functions that describe available data. Notably, e.g. $K$ pressure profiles are spatially more compact than $\pi$ profiles and both achieve near-core pressures of similar magnitude to that found in neutron stars., Comment: 9 pages, 6 figures, 2 tables. Accepted for publication in Phys. Lett. B

A contact interaction is used to calculate an array of pion twist-two, -three and -four generalised transverse light-front momentum dependent parton distribution functions (GTMDs). Despite the interaction's simplicity, many of the results are physically relevant, amongst them a statement that GTMD size and shape are largely prescribed by the scale of emergent hadronic mass. Moreover, proceeding from GTMDs to generalised parton distributions (GPDs), it is found that the pion's mass distribution form factor is harder than its electromagnetic form factor, which is harder than the gravitational pressure distribution form factor; the pressure in the neighbourhood of the pion's core is commensurate with that at the centre of a neutron star; the shear pressure is maximal when confinement forces become dominant within the pion; and the spatial distribution of transversely polarised quarks within the pion is asymmetric. Regarding transverse momentum dependent distribution functions (TMDs), their magnitude and domain of support decrease with increasing twist. The simplest Wigner distribution associated with the pion's twist-two dressed-quark GTMD is sharply peaked on the kinematic domain associated with valence-quark dominance; has a domain of negative support; and broadens as the transverse position variable increases in magnitude., Comment: 20 pages, 12 figures, 1 table

Using lattice configurations for quantum chromodynamics (QCD) generated with three domain-wall fermions at a physical pion mass, we obtain a parameter-free prediction of QCD's renormalisation-group-invariant process-independent effective charge, $\hat\alpha(k^2)$. Owing to the dynamical breaking of scale invariance, evident in the emergence of a gluon mass-scale, this coupling saturates at infrared momenta: $\hat\alpha(0)/\pi=0.97(4)$. Amongst other things: $\hat\alpha(k^2)$ is almost identical to the process-dependent (PD) effective charge defined via the Bjorken sum rule; and also that PD charge which, employed in the one-loop evolution equations, delivers agreement between pion parton distribution functions computed at the hadronic scale and experiment. The diversity of unifying roles played by $\hat\alpha(k^2)$ suggests that it is a strong candidate for that object which represents the interaction strength in QCD at any given momentum scale; and its properties support a conclusion that QCD is a mathematically well-defined quantum field theory in four dimensions., Comment: 10 pages, 4 figures

In this paper, we use the equation of state based on a modification of 2+1 flavors Nambu-Jona- Lasinio (NJL) model to study the quark matter of hybrid stars. For comparison, we utilize five EOSs of the relativistic mean-field (RMF) model to describe the hadronic phase. With the 3- window crossover interpolation approach, we try to construct relatively soft hybrid EOSs but find the maximum masses of hybrid stars do not differ too much. The results are quite close to two solar mass, which is consistent with the mass constraint of PSR J0348+0432. Furthermore it is noteworthy that the heaviest stable stars have central densities higher than that of the deconfinement transition thus suggesting a pure quark core in the hybrid star.

In this paper we use the equation of state (EOS) of 2+1 flavors Nambu-Jona-Lasinio (NJL) model to study the structure of compact stars. To avoid the ultraviolet divergence, we employ the proper-time regularization (PTR) with an ultraviolet cutoff. For comparison, we fix three sets of parameters, where the constraints of chemical equilibrium and electric charge neutrality conditions are taken into consideration. With a certain interpolation method in the crossover region, we construct three corresponding hybrid EOSs but find that the maximum masses of hybrid stars in the three different cases don't differ too much. It should be pointed out that, the results we get are in accordance with the recent astro-observation PSR J0348+0432, PSR J1614-2230, PSR J1946+3417.